In warehousing of heavy articles, there is a continuous need for mobile, lightweight hoist vehicles for placing and removing articles to and from multi-tiered shelves. In the construction of such hoists, consideration must be given to providing a hoist that can be moved along relatively narrow aisles without interferences with overhanging wiring, plumbing and duct work. There are also needs for such hoists to load and unload heavy battery cells on shelves for use as emergency power supplies for telephone exchanges or as energy sources for computer installations. Additionally, such hoists should be easily transportable from one location to another.
Numerous diverse types of lift trucks, mobile hoists and gantry arrangements have been developed to facilitate the placing and removal of heavy objects onto and from multi-tiered shelving. One example of a hoist that has been developed to move round cell batteries onto and from multi-tiered shelving is shown in R. C. French et al. U.S. Pat. No. 3,858,736 issued Jan. 7, 1975. In this patent a castered flat platform supports a rotatably mounted pole from which laterally extends a slide and tong-like clamp assembly. The clamp assembly is movably mounted on the pole so that an article can be lifted and orbited about the pole and then moved over and onto a shelf. Laterally extending foldable, stabilizing arms are provided to counteract forces tending to tilt the hoist during loading and unloading operations.
Another example of a mobile hoist is shown in U.S Pat. No. 4,239,443, issued Dec. 16, 1980 to applicant in the instant application. The mobile hoist described in this patent includes an open frame structure for receiving an article which is clamped, lifted and then moved from within the frame structure onto a shelf.
While the above-mentioned hoists were commercially available and have been utilized in the field with various degrees of success, placement of round cell batteries in space limited quarters requires more and more compact, lighter and easily transportable hoists which are not only powerful enough to lift and lower the round cell batteries but additionally perform the lifting and the lowering actions in a smooth and jerk-free manner. The smooth start-stop actions are difficult, if not impossible to achieve with the above-mentioned hoists.